Cardiac rhythm management (CRM) devices can include implantable devices that provide electrical stimulation to selected chambers of the heart in order to treat disorders of cardiac rhythm. For example, an implantable pacemaker can deliver timed pacing pulses to the heart to treat bradyarrhythmia, in which the heart rate can be too slow. In another example of a cardiac rhythm management device, an implantable cardioversion/defibrillator can deliver antitachyarrhythmia pacing (ATP) or a cardioversion or defibrillation shock to treat tachyarrhythmia, in which the heart rate can be too fast, and can also include pacing capability for bradyarrhythmia. Tachyarrhythmia includes ventricular tachycardia (VT) and supraventricular tachycardia (SVT). Tachyarrhythmia also includes rapid and irregular heart rate, or fibrillation, including ventricular fibrillation (VF). Tachyarrhythmia can also occur in the atria. Examples include atrial fibrillation (AF) and atrial flutter (AFI). In yet another example, implantable cardiac resynchronization therapy (CRT) devices can deliver pacing-level pulses to spatially coordinate the heart contraction (with or without altering heart rate) for obtaining a more efficient contraction to improve cardiac output, and such capability can be combined with pacers, cardioverters, or defibrillators. In an even further example, implantable neurostimulation devices can be used to deliver electrical energy to a desired portion of the autonomic nervous system, such as to stimulate or inhibit one of the sympathetic or parasympathetic nervous systems to adjust an autonomic balance to impact cardiovascular performance.
CRMs are able to communicate with external devices using wireless communication methods such as radio frequency (RF) or mutual inductance. Some CRMs are able to obtain sampled values of the monitored heart activity signals or values of electrical signals provided by a sensor. The sampled heart activity signals are sometimes referred to as an electrogram. An electrogram can be stored in the CRM and later communicated to an external device where the sampled signals can be displayed for analysis. An electrogram can also be communicated to the external device from the CRM as the heart activity signal is sampled to provide real time electrograms. Along with electrogram data many other physiological parameters can be monitored and stored by CRMs (or other types of implantable medical devices). Retaining collected physiological data and presenting it in a meaningful manner to a treating physician can present challenges due to the limited storage and power capabilities present in CRM devices.